What is the Difference Between Ortho Nitrophenol and Para Nitrophenol

Ortho nitrophenol and para-nitrophenol are both derivatives of nitrophenol, which is a compound containing a phenol ring substituted with a nitro group (-NO₂). The main difference between ortho nitrophenol and para nitrophenol lies in the position of the nitro group on the phenol ring.

What is the difference between ortho nitrophenol and para nitrophenol? In ortho nitrophenol, the nitro group is attached to the ortho position, whereas in para nitrophenol, the nitro group is attached to the para position.

Key Areas Covered

1. What is Ortho Nitrophenol  
      – Definition, Features 
2. What is Para Nitrophenol
      – Definition, Features 
3. Similarities Between Ortho Nitrophenol and Para Nitrophenol
      – Outline of Common Features
4. Difference Between Ortho Nitrophenol and Para Nitrophenol
      – Comparison of Key Differences
5. FAQ: Ortho Nitrophenol and Para Nitrophenol
      – Answers to Frequently Asked Questions

Key Terms

2-Nitrophenol, 4-Nitrophenol, C₆H₄NO₃ , C₆H₅NO₃, Ortho Nitrophenol, Para Nitrophenol, O-Nitrophenol, P-Nitrophenol

What is Ortho Nitrophenol

Ortho-nitrophenol (ONP), also known as 2-nitrophenol, is a chemical compound with the molecular formula C₆H₅NO₃. It belongs to the class of aromatic organic compounds and is derived from phenol by the substitution of a nitro group (-NO₂) at the ortho position relative to the hydroxyl group (-OH).

The chemical structure of ortho-nitrophenol gives rise to several interesting properties and reactivities. One notable characteristic is its acidic nature due to the presence of the hydroxyl group. The acidity of ortho-nitrophenol is further enhanced by the electron-withdrawing effect of the adjacent nitro group, making it a stronger acid compared to phenol.

Ortho-nitrophenol exhibits yellow coloration in its pure form, and this color deepens with increasing concentration or acidity. This color change is attributed to the formation of hydrogen bonds between ONP molecules, leading to the aggregation of molecules and consequent alteration in light absorption properties.

In terms of reactivity, ortho-nitrophenol undergoes various chemical transformations. For instance, it can be reduced to ortho-aminophenol (2-aminophenol) using reducing agents like iron and hydrochloric acid. Furthermore, ONP can undergo electrophilic aromatic substitution reactions, where the nitro group serves as a directing group for the introduction of substituents onto the aromatic ring.

Due to its chemical properties and structural features, ortho-nitrophenol finds applications in organic synthesis, particularly in the preparation of dyes, pharmaceuticals, and agricultural chemicals. Additionally, it has been studied for its environmental impact, as it is considered a pollutant in water bodies due to its toxicity to aquatic organisms.

What is Para Nitrophenol

Para nitrophenol (p-nitrophenol or 4-nitrophenol) is a chemical compound with the molecular formula C₆H₄NO_3. It is a pale yellow solid that is soluble in water and most organic solvents. This compound is notable for its diverse applications in various fields, including chemistry, biology, and industry.

One of the key uses of para nitrophenol is as a precursor in the synthesis of pharmaceuticals, dyes, and pesticides. Its chemical structure makes it a valuable intermediate in the production of numerous compounds. In the pharmaceutical industry, it serves as a building block for the synthesis of antibiotics, analgesics, and antipyretics. Additionally, it is utilized in the manufacture of dyes, where it imparts yellow coloration to various products. Furthermore, p-nitrophenol finds application in the synthesis of herbicides and insecticides, contributing to agricultural practices.

In biochemical research, para nitrophenol is employed as a substrate in enzymatic assays. It is commonly used in assays involving β-galactosidase, an enzyme that cleaves p-nitrophenyl-β-D-galactopyranoside (PNPG) to release para nitrophenol. The release of para nitrophenol is detected spectrophotometrically, allowing researchers to quantify enzyme activity and study enzyme kinetics.

Moreover, para nitrophenol has utility in environmental science and water treatment. It is used as an indicator of microbial contamination in water sources due to its reaction with alkaline solutions, producing a yellow coloration. This property enables rapid detection of fecal contamination in water samples, aiding in the monitoring and maintenance of water quality standards.

However, it’s important to note that para nitrophenol is considered toxic and poses health risks to humans and the environment. Exposure to high concentrations can cause irritation to the respiratory tract, skin, and eyes. Therefore, proper handling and disposal protocols must be followed to mitigate potential hazards associated with this compound.

Similarities Between Ortho Nitrophenol and Para Nitrophenol

1. Both compounds have the same chemical formula, C₆H₅NO₃, indicating they have the same number and types of atoms.
2. They both contain a nitro group (NO₂) attached to a phenol ring.

Difference Between Ortho Nitrophenol and Para Nitrophenol

Definition

Ortho nitrophenol is a compound with a nitro group bonded to the same benzene ring at the second position (ortho position) relative to a hydroxyl group, while para nitrophenol is a compound with a nitro group bonded to the same benzene ring at the fourth position (para position) relative to a hydroxyl group.

Structure

In ortho nitrophenol, the nitro group is attached to the ortho position (adjacent carbons) of the phenol ring, whereas in para nitrophenol, it is attached to the para position (opposite carbons).

Acidity

Para nitrophenol is more acidic compared to ortho nitrophenol.

Solubility

Para nitrophenol is generally more soluble in water due to its ability to form intermolecular hydrogen bonds with water.

Boiling Point

Ortho nitrophenol has a lower boiling point due to weaker intermolecular forces.

Melting Point

Ortho nitrophenol has a slightly lower melting point, but para-nitrophenol can be slightly higher in some cases.

Conclusion

In conclusion, ortho-nitrophenol (ONP) and para-nitrophenol (p-nitrophenol) are two derivatives of nitrophenol with distinct molecular structures and properties. While both share the same chemical formula and contain a nitro group attached to a phenol ring, they differ in the position of the nitro group and exhibit variations in acidity, boiling point, and solubility. Ortho-nitrophenol is stabilized by intramolecular hydrogen bonding, making it less acidic and less soluble compared to para-nitrophenol.

FAQ: Ortho Nitrophenol and Para Nitrophenol

1. Why ortho nitrophenol is more stable than para nitrophenol?

Ortho-nitrophenol exhibits greater stability compared to para-nitrophenol due to the presence of intramolecular hydrogen bonding between the hydrogen atom of the hydroxyl group and an oxygen atom of the nitro group. This stabilizing interaction enhances the overall stability of ortho-nitrophenol by promoting stronger intermolecular forces within the molecule, resulting in higher resistance to chemical reactions or structural changes.

2. Which has more boiling point ortho nitrophenol or para nitrophenol?

The boiling point of para-nitrophenol (p-nitrophenol) is generally higher than that of ortho-nitrophenol (o-nitrophenol). This is primarily due to the stronger intermolecular hydrogen bonding present in para-nitrophenol, which requires more energy to overcome during the transition from liquid to gas phase.

3. Which is more acidic?

Para-nitrophenol (p-nitrophenol) is generally more acidic than ortho-nitrophenol (o-nitrophenol). This higher acidity in para-nitrophenol is attributed to the resonance stabilization of the phenolate ion formed upon deprotonation, where the negative charge is delocalized over the nitro group and the phenolate ring.

4. Why does Ortho nitrophenol has a less boiling point than para-nitrophenol?

Para-nitrophenol shows intermolecular hydrogen bonding between molecules, which results in stronger attractive forces between molecules and thus a higher boiling point compared to ortho-nitrophenol. In contrast, ortho-nitrophenol undergoes intramolecular hydrogen bonding within the same molecule, which reduces the overall intermolecular forces and lowers the boiling point compared to para-nitrophenol.

5. Which is less soluble, ortho-nitrophenol or  para nitrophenol?

Generally, ortho-nitrophenol tends to be less soluble in water compared to para-nitrophenol due to intramolecular hydrogen bonding within the ortho isomer, which reduces its ability to form hydrogen bonds with water molecules.

Reference:

1. “2-Nitrophenol.” PubChem. National Library of Medicine.

Image Courtesy:

1. “O-Nitrophenol” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “P-Nitrophenol” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia